CAMBRIDGE, Mass.--(BUSINESS WIRE)--Acceleron Pharma Inc. (NASDAQ:XLRN), a clinical stage biopharmaceutical company focused on the discovery, development and commercialization of novel protein therapeutics for cancer and rare diseases, today announced that its collaboration partner, Celgene, has initiated a phase 2 clinical trial of sotatercept in patients with end stage renal disease on hemodialysis. Sotatercept is a novel and first-in-class activin type IIA receptor (ActRIIA) fusion protein that acts during late-stage erythropoiesis (red blood cell production) to increase the production of mature red blood cells into circulation. Acceleron will receive a $7 million milestone payment from Celgene for the achievement of this event and is also eligible to receive future development, regulatory and commercial milestones of up to $360 million for the sotatercept program.